RU2356133C2 - Water distribution control in fuel cells - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrochemical fuel cells with solid polymeric electrolyte. According to the invention fuel cell comprises anode, ion-exchange membrane and cathode, performed with liquid phase water supply to flow-through grooves for fluid medium formed in cathode so that 100% relative humidity is supported along the whole length of grooves. Invention suggests gaging method and facilities for determination of optimum quantity or quantity interval for liquid phase water which is to be supplied to cathode flow-through grooves for fluid medium when operation conditions change. Also mode of operation and facilities are suggested that provide optimum liquid phase water quantity supply to cathode flow-through grooves for fluid medium when operation conditions are measured.

EFFECT: improvement of fuel cell battery operation.

22 cl, 16 dwg

Description

The present invention relates to electrochemical fuel cells, in particular to solid polymer electrolyte fuel cells, which convert a fuel and an oxidizing agent into electrical energy and a reaction product.

Figure 1 presents a typical layout of the fuel cell 10, and for clarity, this drawing shows the various layers of the construction of the fuel cell in a disassembled form. Between the anode 12 and the cathode 13 is an ion-exchange membrane 11 of a solid polymer. Typically, the anode 12 and cathode 13 are both made of an electrically conductive porous material, for example porous carbon, to which small particles of platinum and / or another precious metal catalyst are attached. The anode 12 and cathode 13 are usually attached directly to the respective adjacent surfaces of the membrane 11. Such a connection of the components of the fuel cell is usually called the membrane electrode assembly, or, abbreviated as MES.

A polymer membrane and layers of porous electrodes are placed between the anode plate 14 to distribute the fluid flow and the cathode plate 15 to distribute the fluid flow. In addition, intermediate protective layers 12a and 13a can be placed between the anode plate 14 for distributing the fluid and the anode 12 and similarly between the cathode plate 15 for distributing the fluid flow and the cathode 13. The protective layers have a porous structure and are made so that they provide effective diffusion of gas to and from the surfaces of the anode and cathode, and also help control the distribution of water vapor and the liquid phase of water.

The fluid distribution plates 14 and 15 are made of an electrically conductive non-porous material, whereby electrical contact can be made with the respective electrodes, the anode 12 or the cathode 13. At the same time, the plates for distributing the fluid flow should facilitate the passage to the porous electrodes and / or removal of fuel, oxidizing agent and / or reaction product from them. This is usually accomplished by forming passages for the fluid flow on the surface of the plates to distribute the fluid flow, for example in the form of grooves or grooves 16 on the surface facing the porous electrodes 12, 13.

In addition, FIG. 2 (a) shows one known configuration of a fluid flow groove that forms a tortuous (serpentine) structure 20 on the surface of the anode 14 (or cathode 15) having an input manifold 21 and an output manifold 22, as shown figure 2 (a). According to the known construction, the serpentine structure 20 is a groove 16 on the surface of the plate 14 (or 15), at the same time, each of the manifolds 21 and 22 includes a hole passing through the plate so that the fluid supplied to or withdrawn from the groove 16 , could pass through the thickness of the plate pack in the direction perpendicular to the plate indicated by the arrow in FIG. 2 (b), which shows a cross section along line AA shown in FIG. 2 (a).

Other openings 23, 25 of the manifolds may also be provided to allow fuel, oxidizer, other fluids, or exhaust gases to enter other grooves in the plates (not shown).

The grooves 16 in the fluid distribution plates 14, 15 can be made open at both ends, i.e. these grooves, passing, as shown, between the inlet manifold 21 and the outlet manifold 22, providing a continuous flow of the fluid, are usually used to supply the oxidizing agent and discharge the reaction product. Alternatively, the grooves 16 may be closed at one end, i.e. each groove is in communication only with the inlet manifold 21 for supplying a fluid based on the full 100% transfer of gaseous matter to or from the porous electrodes of the MES. The groove thus closed can be used to supply hydrogen fuel to the comb-type design elements 11-13 of the MES.

FIG. 3 is a cross-sectional view of a portion of a stack of plates forming a conventional fuel cell assembly 30. In this design, the adjacent anode and cathode plates for distributing the fluid flow are combined in a known manner to form a single bipolar plate 31 having anode grooves 32 on one surface and cathode grooves 33 on the opposite surface, each of which adjacent to the corresponding membrane-electrode assembly (MES) ) 34. All openings 21 of the inlet manifold and openings 22 of the outlet manifold are combined to form the inlet and outlet manifolds for the entire fuel cell battery. The various components of the fuel cell battery in the drawing are shown slightly separated from each other, although it is clear that, if necessary, they will be pressed against each other using gaskets.

To achieve high efficiency and duration of energy supply from the fuel cell, it is mainly necessary to maintain a high moisture content inside the membrane-electrode assembly and, in particular, inside the membrane.

In the prior art, this is usually achieved by humidifying the supplied gases, namely fuel, air, or both, coming through the collectors 21, 22 or 23 and through the grooves 16. In other words, water is supplied to the grooves 16 in the vapor phase (hereinafter referred to as the "vapor phase of water "). This, in addition, can contribute, to a limited extent, to the distribution of heat fluxes within the fuel cell unit.

Another method is to supply water in a liquid phase (hereinafter - the "liquid phase of water") directly to the membrane 11, 34, for example directly to the surfaces of the electrode or into the grooves 16 of the bipolar plates 31. The advantage of this method is not only the amount of water required to maintain its high content in the membrane, but also in the possibility of significant cooling of the fuel cell due to evaporation and the release of latent heat of vaporization. In detail, a method for supplying a liquid phase of water directly to the surfaces of an electrode or into grooves 16 is disclosed in international application PCT / GB03 / 02973 (not published at the filing date of this application). Therefore, in this description, where it relates to the disclosure of the invention, the relevant parts of said patent document are reproduced.

This method of direct removal of heat, which provides the removal of thermal energy by means of the outgoing gas stream, has a clear advantage associated with the possibility of excluding cooling plates from the battery of fuel cells.

An object of the present invention is to provide a method and apparatus for improving the operation of an evaporative-cooled fuel cell battery by introducing excess water into the grooves 16 of the cathode electrode.

In accordance with one aspect, the present invention relates to a method for operating an electrochemical fuel cell comprising an anode, an ion exchange membrane and a cathode, comprising the steps of

the supply of fluid fuel in the flow grooves for the fluid, made in the anode;

supplying a fluid oxidizing agent to the fluid flow grooves made in the cathode;

removal of reaction by-products and unused oxidizing agent from fluid flow grooves made in the cathode; and

supplying a sufficient amount of a liquid phase of water to the flow grooves for the fluid inside the cathode so that a relative humidity of 100% is maintained substantially along the entire length of the grooves for the fluid.

In accordance with another aspect, the present invention relates to an electrochemical fuel cell system comprising

at least one anode plate for distributing a fluid flow, in which there are flow grooves for the fluid,

at least one ion exchange membrane

at least one cathode plate for distributing a fluid flow, in which there are flow grooves for the fluid,

means for supplying fluid fuel to the anode flow grooves for the fluid,

means for supplying a fluid oxidizing agent to the cathode flow grooves for the fluid,

means for introducing water to supply a sufficient amount of a liquid phase of water to the flow grooves for the fluid made in the cathode, so that essentially 100% relative humidity is maintained throughout the length of the grooves for the fluid under normal operating conditions of the fuel cell.

Exemplary embodiments of the present invention will be disclosed in the following description by way of example and with reference to the accompanying drawings.

Figure 1 is a schematic cross-sectional view of a portion of a known fuel cell.

FIGS. 2 (a) and 2 (b) are plates of the fuel cell shown in FIG. 1 for distributing a fluid flow, a schematic plan view and a sectional view.

Figure 3 is a known fuel cell battery with bipolar plates, cross section.

Figure 4 (a) is a plate for distributing a fluid flow of a fuel cell made with a serpentine channel for a fluid flow, a plan view showing the location of the contours of the foil for the distribution of water and the protective foil.

Fig. 4 (b) is a plate for distributing a fluid flow of a fuel cell made with a counter-comb structure of a channel for a fluid flow, a plan view showing the arrangement of the contours of the foil for the distribution of water and the protective foil.

5 is a foil for the distribution of water, a plan view.

6 is a plate for distributing a fluid flow, a foil for distributing water and a covering foil, in accordance with figure 4 and figure 5, a cross section.

Fig.7 is a part of the prefabricated structure shown in Fig.6, a perspective view.

Fig. 8 is a transverse sectional view of a plate for distributing a fluid flow with a reversed mutual arrangement of foil for distributing water and a coating foil.

Fig.9 is a schematic view in plan of the points of entry of water for the grooves of the anti-comb structure.

10 is a diagram illustrating the principles of water cooling of a cathode of a fuel cell.

11 is a graph illustrating the change in mass of the vapor phase of water, referred to a unit mass of air, depending on temperature for full saturation conditions, i.e. at a relative humidity of 100%.

12 is a graph illustrating a change in voltage of a fuel cell battery depending on a flow rate of a liquid phase of water supplied to a cathode.

13 is a graphical dependence illustrating a theoretical minimum water flow rate as a function of the current of a fuel cell battery.

Fig. 14 is a block diagram of a system with a fuel cell battery including a water supply control system.

During the operation of the assembled battery 30 of fuel cells, heat is generated in it due to electrochemical and electrical losses. In one exemplary embodiment of the evaporative cooling fuel cell 10 included in the battery shown schematically in FIG. 10, this heat is removed due to the temperature of the waste products 100, 101 being higher than the inlet temperature of the reactants 102, 103, and due to the evaporation of liquid phase of water 104 supplied to the cathode 13 and evaporated in the air stream 103 entering the cathode. It has been established that at all levels of energy generation, with the exception of the lowest, evaporative cooling is the predominant mechanism of heat removal.

The liquid phase of water 104 will evaporate if the partial pressure of the vapor phase of water in the air stream passing through the cathode is sufficiently low, i.e. evaporation will occur in such conditions when the relative humidity is less than 100% and heat is supplied to evaporate the liquid phase of water. As soon as local conditions become such that the relative humidity of the water is 100%, i.e. the air is saturated with water vapor, further evaporation will not occur until one of the following three conditions is met: (i) the air flow rate is increased so that the partial pressure of the vapor phase of the water decreases inversely proportional, (ii) the total pressure decreases so that the partial pressure of the vapor phase of the water decreases proportionally, (iii) the local temperature increases, which leads to a shift in the point of thermodynamic equilibrium, and as a result, evaporation can occur for another until air is completely saturated with moisture.

Thus, for a fuel cell 10 operating under excess water at each point of the cathode 13 in the battery 30 of fuel cells, as well as at a constant pressure and constant air flow at the cathode, the conditions of local equilibrium are such that the air is completely saturated with water vapor, and any additional heat removal through evaporation can be carried out only by increasing the local temperature.

The actual increase in temperature for the implementation of the evaporation process and, consequently, the cooling of the fuel cell depends on the sensitivity of the evaporation equilibrium point under the prevailing operating conditions and the required degree of cooling. 11 qualitatively illustrates the change in mass of the vapor phase of water, referred to a unit mass of air, with a change in temperature for conditions of complete saturation, i.e. in conditions of 100% relative humidity and constant total pressure. Thus, the operating temperature of the battery is largely determined by the evaporation rate necessary for the implementation of the cooling process, the total pressure and the mass flow rate of the air flow at the cathode.

As shown in FIG. 11, at a higher temperature, a small increase in temperature ΔT leads to a significant increase in Δm, i.e. mass of the vapor phase of water, which may be contained in the air stream, and, consequently, to an increase in the mass of evaporated water, which may occur as a result of heat generation inside the fuel battery. As a result, the temperature of the fuel battery over a wide range of heat loads will remain approximately constant both as a whole (i.e., depending on the change in the total energy of the fuel battery) and locally (due to changes in the local heat generation due to the non-uniform temperature inside the battery at this total battery power). This leads to a high degree of implicit regulation at the operating temperatures of the battery and leads to a good thermal balance maintained throughout the battery.

In addition, the presence of excess water in the individual grooves 16 or flow channels of the prefabricated design of the battery 30 of the fuel cells allows for indirect control of air flow in each channel in the following way. If in a certain channel the air flow exceeds the average flow rate, then in this case, for the purpose of additional cooling, if necessary, additional water can be evaporated into the air flow. This leads to an increase in the volumetric flow rate at the outlet of the flow channel above the average level, which, under the conditions of the same pressure drop across all flow channels, limits the air flow in the fuel cell channel, providing implicit air flow control with improving the thermal balance of the battery and, therefore, improving the voltage balance in the fuel cells of a battery. The same pressure drop across all grooves 16 is usually achieved by choosing the ratio of the sizes of the manifolds 21, 22 and grooves 16.

Indirect control of the battery temperature can be implemented, if necessary, by reducing the air flow supplied to the cathode, and / or by changing the total pressure of the air flow supplied to the cathode. In other words, air flow can be increased for this purpose, which leads to a decrease in the partial pressure of water vapor by increasing the total volume of air into which water can evaporate. Therefore, additional water can be evaporated until saturation is achieved, which provides additional cooling and reduces the operating temperature of the fuel battery.

Alternatively or additionally, the outlet pressure may be reduced. By reducing the total pressure, the partial pressure of water vapor will decrease. This causes a shift in the point of thermodynamic equilibrium so that an additional amount of water can be evaporated before the saturation state occurs, thereby creating additional cooling and leading to a decrease in the operating temperature of the battery.

Other parameters, such as the flow rate of the fluid at the anode, the inlet temperature of the fuel and oxidizer, surface leakage, etc., have been found to be less important.

In a preferred embodiment of the system, which is preferably not under pressure, a typical operating temperature of a fuel cell stack is from 70 to 80 ° C. However, in principle, this temperature can vary in the range from 65 to 95 ° C due to the regulation of air flow and / or the total pressure of the air flow at the anode. At low power levels, when evaporative cooling is not the dominant process, the operating temperature of the battery can be significantly lower. The functioning of the system at higher or lower pressures allows you to significantly change the boundaries of the temperature ranges indicated above.

In practice, the average temperature of the reagents and the liquid phase of the water introduced into the battery of the fuel cells may be lower than the operating temperature of the battery. Therefore, some degree of cooling will be achieved by heating these inlet streams to the operating temperature of the fuel battery. When the incoming flows reach the operating temperature of the battery, the rest of the cooling will be ensured due to the evaporation of the liquid phase of water into the air stream at the cathode. The proportion of evaporative cooling depends on a number of factors, including cathode air flow, water flow, fuel cell battery power and temperature of the incoming fluid flows. In most cases, evaporative cooling is the predominant mechanism of the cooling process, leading to the high efficiency of the aforementioned indirect temperature control. However, in cases where the average temperature of the incoming fluid flows is lower than the operating temperature of the fuel battery, a temperature difference will exist in the area of the battery into which the reagents and the liquid phase of the water enter.

In order for evaporative cooling to be effective, a sufficient amount of the liquid phase of water must be present in each part of the fuel cell stack. In the event of a lack of water, the energy performance of the battery will deteriorate with potentially serious negative consequences.

Possible problems include the following: (i) drainage of the membrane, which leads to a decrease in voltage on the corresponding fuel cell, (ii) hot spots caused by the lack of a liquid phase of water and, therefore, insufficient evaporative cooling, which will damage the membrane and shorten its life .

To provide sufficient water for evaporative cooling, the following alternative methods can be used: (i) accurate dosing of the liquid phase of the water supplied to the cathode, so that its amount is just sufficient to maintain a relative humidity of 100% over the entire surface of the cathode and in each fuel cell of the battery of fuel cells, or (ii) supplying an excess amount of the liquid phase of water to the entire battery so that the excess water is constantly maintained over the entire surface of the cathode and in each fuel om battery cell of the fuel cell. To ensure the necessary supply of liquid water to the cathode, each and any cathode groove 16 may have water entry points, as will be shown below.

In current fuel cells, it is difficult to accurately meter liquid water to each component of a fuel cell stack. In addition, manufacturing tolerances and heterogeneous operating conditions cause different requirements for cooling in each section of the battery of fuel cells, which increases the difficulties associated with the need for accurate dosing.

Therefore, supplying the cathode with water with such an excess that its excess at the cathode always takes place in each area inside the battery is the preferred method, since it avoids the drying of the membrane, the appearance of hot spots and leads to improved battery performance and longer battery life.

So, according to one main aspect of the invention, supplying the excess liquid phase of water to the cathode allows maintaining a relative humidity of 100% in the cathode over substantially the entire length of the flow grooves for the fluid.

In accordance with another aspect of the invention, when the fuel cell is operating, the supply of the liquid phase of water to the cathode and / or the gas flow through the cathode for any measured power removed from the fuel cell is controlled so that the amount of the liquid phase of water is greater in all sections of the cathode surface, than can be evaporated at existing temperature and pressure.

According to yet another aspect, the above fuel cell operating conditions are applied to a plurality of such fuel cells included in a fuel cell battery having a common oxidizer supply manifold and a common water inlet collector, so that for any measured power removed from the fuel cell battery, a liquid feed the phases of the water into the water inlet collector and / or the gas flow rate through the oxidizer supply manifold are controlled so that the amount of liquid PS was more water than can be evaporated under the existing temperature and pressure.

For a practically used battery, which is characterized by real existing inhomogeneities, under normal operating conditions and a water coefficient of less than unity, it should be taken into account that some battery cells can receive a smaller amount of the liquid phase of water than is necessary to maintain a relative humidity of 100% at the cathode, substantially the entire length of the flow grooves for the fluid at the cathode. Accordingly, some battery cells can receive a larger amount of the liquid phase of water than is required to maintain a relative humidity of 100%, essentially along the entire length of the flow channels for the fluid in the cathode. Therefore, according to another aspect of the invention, the excess supply of the liquid phase of water to the battery is selected so that all the components of this battery receive at least the minimum amount of liquid phase of water necessary to maintain a relative humidity of 100%, essentially along the entire length of the flow channels available in the cathode, which corresponds to the water coefficient of the fuel cell battery is greater than one.

12 qualitatively illustrates the variation in the voltage of the fuel battery depending on the flow rate of the liquid phase of the water supplied to the cathode for a typical fuel cell battery operating with evaporative cooling operating at a constant current value and a constant air flow rate at the cathode. At low water flow rates, the total voltage of the battery decreases, indicating that some battery cells may not receive enough liquid phase water to provide adequate cooling and / or adequate hydration of the membrane. With increasing water consumption, the maximum value of the battery voltage is reached (shown at 120), while water is supplied in excess to all components of the fuel cell battery. At higher water flow rates, the battery voltage gradually decreases, possibly due to a decrease in the resulting partial oxygen pressure in the air stream (replaced by water) at the cathode and / or possibly as a result of blocking the transfer of gas to or from the membrane due to the presence of water.

In addition, at higher water flow rates, the balance of fuel cells (as shown by monitoring the voltage on the fuel cells) may deteriorate, thereby showing the value of the upper limit of the maximum water coefficient that can be implemented for a given battery. In addition, it may be that the maximum flow rate is determined by the maximum achievable flow rate using a suitable water pump.

Despite these limiting factors, it was found that a large working area can be allocated within which significant amounts of excess water can flow to the cathode, providing sufficient hydration and cooling of each component of the fuel cell battery.

The amount of water supplied to the cathode is useful to present as a multiple of the theoretical minimum amount required for evaporative cooling, i.e. thereby determines the "water coefficient" VK

VK = m _w / m _w (minimum)

where m _w is the mass flow rate of the supplied liquid phase of water, and m _w (minimum) is the theoretical minimum flow rate of the liquid phase of water, calculated in accordance with the procedure below.

The theoretical minimum amount of water needed for evaporative cooling can be calculated by compiling the heat balance for the fuel cell and assuming that

(i) the enthalpy of the reaction is equal to the low calorific value of the fuel, since the vapor phase of the water is produced as a product (in the absence of excess water);

(ii) the thermal load on the fuel cell is determined on the basis of experimental data on productivity (reaction output) depending on the current of the fuel battery;

(iii) the heat load is equal to the increase in the enthalpy of the reaction products with respect to the enthalpy of the starting reagents, including the complete evaporation of the liquid phase of the water supplied to the cathode.

Therefore, the actual water coefficient for a given operating point can be defined as a multiple of this value.

It should be borne in mind that the water coefficient can be obtained by other methods compared to those described above, the use of which can give slightly different preferred ranges of the water coefficient corresponding to its definition here.

13 schematically shows the theoretical minimum flow rate of the liquid phase of water depending on the battery current, i.e. the location of the points for the water coefficient equal to unity, indicated in the drawing by the line WF = 1. With increasing battery current, the required water flow increases non-linearly, as at higher currents, the efficiency of the battery decreases, which leads to a nonlinear increase in the amount of heat released.

As noted above, the inhomogeneities in the battery and their effect on water consumption at optimal performance (in Fig. 12 corresponds to the area between lines 121 and 122) dictate the need for a real fuel cell battery to function, in which it is not possible to separately meter water into the battery in each point, with a minimum value of the water coefficient, which allows a certain limit of these inhomogeneities. In other words, the water coefficient to be realized must be sufficiently greater than one to ensure a relative humidity of 100% for all fuel cells of the battery and all components of each fuel cell. The maximum value of the water coefficient used is dictated by the maximum acceptable drop in battery performance. The preferred lower and upper limits of the water coefficient WF depending on the battery current are qualitatively shown in FIG. 13 by dashed lines 130 and 131.

The upper and lower limits of water coefficient 130 and 131 can be determined by testing or calibrating a suitable fuel cell battery 30. The calibration of the battery can be carried out by changing the flow rate of water entering the cathode operating at a constant current value and a constant stoichiometric amount of air, in order to determine the minimum water flow rate shown by line 121 and the maximum water flow rate shown by line 122. This calibration is repeated in the interval possible battery currents (and possibly in the range of allowable stoichiometric amounts of air), which will correspond to the normal range of battery operating conditions. Thus, the calibration sets the upper and lower limits of the water coefficient depending on the battery current.

As used herein, the term "stoichiometric amount of air" means the amount of oxygen supplied to inlet 103, normalized to the amount of oxygen consumed in the electrochemical reaction. Thus, with a stoichiometric amount of air equal to 1, all the oxygen in the air combines with hydrogen to form water. With a stoichiometric amount of air equal to 2, 50% of oxygen is consumed in the fuel cell 10 and 50% is contained in the stream at the exit 101 from the cathode. The amount of oxygen required for the reaction is directly dependent on the battery power, efficiency batteries and energy changes as a result of reactive interaction.

In the context of mass production, it is also possible to test a number of representative batteries so that a single set of tolerances can be established with acceptable margins of error that will be suitable for all fuel batteries in a given series.

In a preferred embodiment, the air flow rate 103 at the cathode is controlled in proportion to the current of the battery so that the battery operates with a stoichiometric amount of air of approximately 2 as determined by the requirements of electrochemical processes. In practice, however, the air flow at the cathode can be changed so that the stoichiometric amount of air is in the range from 1.1 to 10, and more preferably in the range from 1.4 to 4, depending on the specific requirements for a given fuel cell battery. At low currents and, consequently, low consumption of reagents in the fuel cell, the stoichiometric amount of air can be significantly higher than these values, since the minimum air flow rate is limited by the minimum flow rate provided by the air compressor.

In a preferred embodiment of the invention, it has been found that the water flow is a linear function of the battery current, which is shown schematically in FIG. The water coefficient for this control method typically ranges from 1.5 to 40, more preferably from 3 to 6.

In practice, the water coefficient can be selected any in the range from 0 to 40 depending on the operating conditions of the battery and the permissible maximum deterioration of the battery due to excess water (see Fig. 12). For example, if the battery operates at a low output power or starts in cold conditions and, therefore, does not reach the maximum operating temperature, in order to temporarily increase the heating rate of the battery, the water flow rate can be set with a low water coefficient or reduced to zero.

In order to indicate the operating temperature of the battery and to carry out a feedback control process of the water supply pump, continuous monitoring of the output temperature at the cathode can be carried out. Thus, in one aspect, this system can temporarily supply a certain amount of water to the fluid flow grooves within the cathode so as to maintain a relative humidity of less than 100% (water coefficient less than unity) if the exit temperature is the cathode below a predetermined threshold corresponding to an insufficiently optimal operating temperature, or during a predetermined period of time following the cold start of the fuel cell.

A metering pump, a flow control unit, or a pressure control method can be used to control the water supply. At low power levels, the required amount of water may be lower than the minimum flow rate that can be obtained using the water pump used. Therefore, at low power levels, a minimum water flow rate can be set to match the set minimum voltage for the water pump to prevent pump breakdown. This is shown schematically in FIG. 13 for current values less than I _crit .

It should be taken into account that the amount of water supplied to the fuel cell battery can, in principle, correspond to some current dependence, provided that the water flow rate is between the minimum and maximum levels of the water coefficient, determined by calibrating the corresponding fuel cell batteries or a number of typical fuel cell batteries.

Since the method of controlling the magnitude of the water coefficient has certain boundaries, additional flexibility in the implementation of cooling can be achieved by controlling the air flow at the cathode and / or the total air pressure at the cathode.

In addition to the above, the battery can be configured to continuously monitor the voltage of the fuel cells so that the operating voltage serves as an indicator of a shortage or excess of water, with the necessary regulation being carried out in real time.

An example of a control system for a water system in a fuel cell battery is disclosed below with reference to FIG.

The fuel cell system 140 includes a fuel cell battery 30 provided with a fuel supply line 102, an anode exhaust line 100, an air supply line 103, a water injection line 104 and a cathode drain line 101. A fuel supply line extends from a fuel source 141, possibly through a humidifier 142 in accordance with well-known principles. The drainage line 100 from the anode can be connected directly to the environment 143, or at least partially in accordance with known principles, the flow can be recycled using the recirculation control circuit 144 for this. The air supply line 103 is supplied by an air compressor 145. The water injection line 104 is supplied by a water pump 146. Water can be supplied from an appropriate source of purified water or can be recycled from the cathode output through a suitable cooler (not shown). A line 101 for diverting the flow from the cathode can be directed into the environment and preferably includes an output sensor 147 that measures at least the output temperature.

A pump 148 may be connected to the cathode output to reduce and / or control the pressure at the cathode output. Pump 148 may be used in addition to or instead of providing compressed air from compressor 145, i.e. otherwise, air may also be supplied at atmospheric pressure.

In addition, the fuel cell system 140 comprises a control unit 150 that preferably receives input signals from sensors corresponding to a battery voltage 151, a battery current 152, and an output temperature 153. The control unit 150 may also be connected to the air through appropriate control signal transmission lines. compressor 145 and pump 146 for supplying water.

The control unit 150 may be configured to operate in two modes.

In the first mode of operation, the control unit 150 may be adapted to obtain calibration data used for the subsequent operation of the fuel cell battery 30. In calibration mode, the control unit 150, by means of a pump 146, changes the flow rate of water that is supplied to the battery under conditions of constant inlet air pressure and constant current drainage from the battery of fuel cells, and also receives measured voltage signals of the battery to determine the corresponding minimum and maximum levels water coefficients 121 and 122 (Fig. 12). Voltage measurement data is stored in calibration table 154. Calibration can be repeated for one or more different current loads, different air inlet pressures, and different stoichiometric amounts of air in order to accumulate a series of comprehensive comprehensive data suitable for controlling the water supply to the battery in the operating area fuel cell modes.

In the second operating mode, the control unit 150 is adapted to use the obtained calibration data accumulated in the calibration table 154 in order to maintain optimal operating conditions of the fuel cell battery. For example, the control unit 150 is adapted to continuously monitor the voltage and current of the battery and control the water supply pump 146 (and possibly an air compressor) to maintain an appropriate water coefficient at the optimum fuel cell performance. In preferred systems, the water coefficient is from 1.5 to 40, more preferably from 3 to 6.

As noted above, the control unit can also use a sensor 147 to monitor the temperature of the exit from the cathode and provide a small amount of water when the temperature at the exit of the cathode is below a pre-selected threshold value corresponding to an insufficiently optimal operating temperature, for example, in the process of starting the fuel cell. In another example, the regulation of the specified stage of "warming up" can be done using a time relay, and not according to the output temperature.

In the embodiment illustrated in FIG. 14, the control unit is adapted both to perform initial calibration of the fuel cell battery and to maintain optimal current operating conditions. However, it was found that for fuel cells of a known type or pre-calibrated systems, the calibration table 154 can be preloaded with data obtained from the operation of the battery for use in the water consumption control unit 150.

Although the embodiment of the invention illustrated in FIG. 14 demonstrates “global” regulation of the fuel cell battery 30 by the control unit 150, it should be understood that more precise regulation can be achieved when water can be supplied to various fuel cells or to various groups of fuel cells. For example, if the system has a large number of independently adjustable places for introducing water into the fuel cell battery, then voltage and current can be separately measured in order to produce local changes in the water supply to each part of the fuel cell battery.

It is possible to use a number of devices that supply a strictly controlled amount of the liquid phase of water to the flow grooves made in the cathode plates to distribute the fluid flow. Such typical devices are disclosed in PCT / GB / 02973 (as of the filing date of this application is not published), and their detailed description is given below with reference to figures 4-9.

In accordance with FIG. 4 (a) and FIG. 4 (b), the present invention provides for a series of water supply channels extending between the water inlet manifold 25 and the individual grooves 16 formed in the plates 40a and 40b for distributing the fluid flow. Generally speaking, the water supply channels are formed by a membrane or a layered structure placed on the surface of the plate 40 for distributing the flow of fluid water. The water supply channels have inlet openings in communication with the inlet manifold 25 for water, and outlet openings, which in the plate for distributing the fluid flow define the boundaries of the preliminary selection of the places of water supply to the grooves 16.

In a preferred embodiment, the layered structure is two layers of foil 41, 42 covering the plate 40, the position of which is shown in figure 4 (a) and figure 4 (b) with dashed lines.

Fig. 4 (a) is a plan view of a fluid distribution plate 40a with a serpentine groove 16 coated with a foil 41a and a foil 42a having first edges 43a, 44a that are aligned with the water inlet manifold 25 and second edges 45a, 46a located at or near a location in a preselected location 49 of the groove 16 in which the water is supplied.

4 (b) illustrates a plan view of a fluid flow distribution plate 40b formed with two counter-comb structures of 47.48 grooves, each of which communicates with a respective manifold 21, 22. The plate is provided with foil 41b and foil 42b, the first edges 43b, 44b of which are aligned with the inlet manifold 25 for water, and second edges 45b, 46b are located at preselected locations of the groove 47 in which the water is supplied, or near these supply points. It should be noted that these two foils can be duplicated on the opposite edge of the plate 40b between the second inlet collector 25 for water and the pre-selected places of water inlet on the groove 48.

FIG. 5 is a detailed plan view of a configuration of a water distribution foil 41 illustrating preferred paths of water supply channels 50. The channels 50 are formed by the first row of grooves 51, which extend from the first edge 43 of the foil 41, located at the inlet collector 25 for water, to the gallery or a small space 52, which distributes water by pressure and placed along the length of the foil 41. The distribution gallery 52 communicates with the second row grooves 53 that extend to the second edge of the foil 45 to communicate with grooves 16 formed in the fluid distribution plate. To implement this message, the second row of grooves 53 is grouped so that they end with corresponding converging configurations 54 at the second edge 45 of the foil 41 serving to supply water.

In the illustrated preferred embodiment, the converging configurations of the 54 grooves end in arched recesses 55 cut in the second edge 45 of the foil 41 at the water inlet points 49, which correspond to preselected locations on top of the grooves 16 shown in FIG. 5 by contour lines.

The pressurized water distribution gallery 52 preferably includes a group of interconnected grooves 56 that divert the incoming water stream from the first row of grooves 51 and efficiently distribute it along the entire length of the foil 41 so that essentially water flows from each group of the second row of grooves 53 the same pressure.

The coating foil 42 shown in FIGS. 4 (a) and 4 (b) is a foil without a relief structure (i.e., without grooves) having a substantially identical external profile with the bottom foil. The coating foil 42 extends beyond the edges of the distribution foil 41, at least at the ends of the second row of grooves, to ensure that water is directed downward into the desired groove 16 of the distribution plate. Most conveniently, such an overlay of one foil on another is achieved by a recess 55 formed in the distribution foil 41, and not in the cover foil 42. Thus, as best seen in the enlarged cross-sectional image in Fig. 6, the cover foil 42 forms an upper cover a sealing element for grooves 51, 52 and 53 to form channels 50 for supplying water, and the ends of the grooves 51 and 53 remain open. In the present embodiment, the coating foil 42 may be slightly larger than the distribution foil 41 so that it overlaps the second edge 45 (and possibly the first edge 43) to obtain the same result.

It should be noted that the foil layers are made very thin compared to the thickness of the plate 40 and are easily placed inside the membrane-electronic assembly 34 in the presence of any gasket placed between the plates. 6, for clarity, these elements are shown with a slight separation, although assembled, of course, they will be pressed against each other.

7 schematically shows the perspective of a water distribution foil 41 placed over a plate 40 for distributing a fluid flow, and shows the combination of various grooves and manifolds.

It should be noted that the distribution grooves 51, 52 and 53 do not have to be formed in the lower foil 41. In another embodiment shown in FIG. 8, the distribution grooves 80 are formed on the lower surface of the upper foil 82, while the lower foil 81 serves as an element covering grooves 80 to form flow channels for supplying water. In other words, the distribution foil 82 and the covering foil 81 in this embodiment are interchanged in comparison with the embodiment shown in FIG. 6.

In the embodiment shown in FIG. 8, at least the second row of grooves (compared to grooves 53 in FIG. 5) does not exactly reach the second edge 83 of the upper foil, but ends at points close to the second edge. The lower (covering) foil 81 will extend almost to the end of the grooves 80, but it will preferably end a little earlier than these grooves so that fluid is able to communicate between the end of the groove 80 and the plate groove 16 at the water inlet 49.

As noted above, the lower (covering) foil 81 closes the grooves 80, forming a barrier to prevent water from flowing out of them into the underlying grooves 16, which are present in the plate 40 for distributing the fluid flow, in places not provided, for example, where water supply channels grooves 16 cross for fuel and / or oxidizer to flow (for example, at point 85).

Preferably, both of the foils described above are made of metal, for example stainless steel. However, any suitable metal having appropriate properties for holding water under pressure can be used, and the term “foil” used in the text of the description of the present invention should be interpreted accordingly. Preferably, the foils are electrically conductive, however, this is not necessary since they do not extend into the MES working area.

In a preferred embodiment, the fluid grooves 16 in the anode or cathode plates 40 typically have a width and depth of 0.4 mm to 1.2 mm. It was found that the width and depth of the groove chemically etched in the foil for water distribution, of the order of 10 μm, is sufficient to ensure the supply of water in the required amount.

In practical use, the pressure of the water supplied through the manifold 25 is adjusted to create a significant difference between the water supply pressure and the gas pressure in the grooves 16 for distributing the fluid, achieving uniform distribution of water across the thousands of channels through which it flows. In a preferred embodiment, water is supplied to the collector at a water pressure according to a pressure gauge in the range of 0.5 to 3 bar.

The advantage of this approach to solving the problem lies in the fact that the described membrane for the distribution of water has an extremely small thickness and can easily be placed inside the existing volume in bipolar plates or in the areas of the gaskets.

The accuracy of the volumetric distribution of water can also be quite strictly regulated using a suitable channel configuration and groove size.

As shown in FIG. 9, water that is distributed over the grooves 90 of the counter-comb structure in the fluid distribution plate 40 may be introduced either at location 91 of the inlet portion of the groove, behind the supply groove 92, or, alternatively, into the outlet end 93 of the groove, at point 94, located at the same end of the bipolar plate where the inlet water collector is located.

The advantage of supplying water to the outlet portions of the groove is to reduce the pressure drop in the reactant gas streams. This is due to the fact that water does not pass through the diffusion material and does not overlap the pore volume for gas passage. In addition, the non-passage of water flow through the diffusion material will also reduce the abrasion of this material, its gradual crushing and structural damage.

The process of evaporative cooling effectively operates in the outlet sections of the grooves, and the water content in the membrane is maintained due to the saturation of air with water vapor.

It should be noted that, within the scope of the claims, other embodiments of the invention are provided.

Claims (22)

1. The method of operation of a battery of electrochemical fuel cells containing many cells, each of which includes an anode, an ion-exchange membrane and a cathode, comprising the steps of supplying fluid fuel to the flow grooves for the fluid located in the anodes, supplying the flowing oxidizer to the flow grooves of the fluid media located in the cathodes, removal of reaction by-products and unused oxidizing agent from the fluid flow grooves located in the cathodes, determining the maximum battery voltage or each fuel cell, depending on the flow rate of the liquid phase of water for each of the many values of the currents of the battery or fuel cell, which correspond to the normal range of operating conditions of the battery or fuel cell, determining a calibration function that reflects the dependence of the minimum flow rate of the liquid phase of water on current and / or stoichiometric amount air and water supply with at least the specified minimum flow rate of the liquid phase of the water required for the current drawn from the specified battery or each fuel about the element, and / or stoichiometric amount of air, determined from the calibration function, into the fluid flow grooves located in the cathode, so that a relative humidity of 100% is maintained along the entire length of the fluid grooves for the fluid. 2. The method according to claim 1, characterized in that it further includes the step of increasing the amount of the liquid phase of the water supplied depending on the current value of the fuel cell or the fuel cell battery, in order to maintain the water coefficient WF> 1.0 for all current values within areas of normal operation of a fuel cell or battery. 3. The method according to claim 1, characterized in that the calibration function is determined for the stoichiometric amount of air in the range from 1.1 to 10. 4. The method according to claim 3, characterized in that the calibration function is determined for the stoichiometric amount of air in the range from 1.4 to 4.0. 5. The method according to any one of claims 1 to 4, characterized in that the step of supplying a sufficient amount of the liquid phase of the water comprises supplying it with a water coefficient of at least 1.5. 6. The method according to claim 5, characterized in that the step of supplying a sufficient amount of the liquid phase of the water comprises supplying it with a water coefficient of at least 3. 7. The method according to claim 5 or 6, characterized in that the step of supplying a sufficient amount of the liquid phase of the water comprises supplying it with a water coefficient of less than 40. 8. The method according to claim 7, characterized in that the stage of supplying a sufficient amount of a liquid phase of water includes its supply with a water coefficient in the range from 3 to 6. 9. The method according to claim 1, characterized in that it includes the step of temporarily supplying such an amount of a liquid phase of water to the flow grooves for the fluid, made in the cathode, so that the relative humidity is maintained at less than 100%, in the case when the outlet temperature from the cathode below a predetermined threshold value corresponding to an insufficiently optimal operating temperature. 10. The method according to claim 9, characterized in that it is used when starting the fuel cell or battery of fuel cells. 11. The method according to claim 1, characterized in that the fuel cell operates in such a way that for any measured output power, the supply of the liquid phase of the water to the cathode and / or the gas flow through the cathode is controlled so that in all areas of the surface of the cathode of the liquid phase of water more than it can evaporate under the most likely conditions of temperature and pressure. 12. The method according to claim 11, characterized in that it is used for a plurality of fuel cells included in a fuel cell battery having a common oxidizer supply manifold and a common water supply collector, so that for any measured output power of the battery, the liquid water phase is adjusted to inlet collector for supplying gas and / or gas flow to the oxidizer supply manifold so that in all zones of the surface of the cathodes of all fuel cells the liquid phase of the water is larger than it can evaporate at the most probable conditions under temperature and pressure. 13. An electrochemical fuel cell system comprising a fuel cell battery including a plurality of fuel cells, each fuel cell comprising an anode plate for distributing a fluid flow, in which flow grooves for a fluid are provided, an ion-exchange membrane, a cathode plate for distributing a fluid flow in which the flow grooves for the fluid are made, the system further comprising means for supplying fluid fuel to the anode flow grooves for t fluid medium; means for supplying a fluid oxidant to the cathode flow grooves for the fluid; means for supplying water for supplying a sufficient amount of the liquid phase of the water to the flow grooves for the fluid located in the cathode; means for determining the maximum voltage of the battery or each fuel cell depending on the flow rate liquid phase of water for each of the many currents of the battery or fuel cell, which correspond to the normal range of operating conditions of the battery or fuel cell, means for op determining a calibration function that reflects the dependence of the minimum flow rate of the liquid phase of water on the current and / or stoichiometric amount of air, and a control unit configured to control the water supply means for supplying water with at least the minimum flow rate of the liquid phase of water required for current discharged from said battery or each fuel cell, and / or for a stoichiometric amount of air determined from the calibration function, so that along the entire length of the flow grooves for fluid During normal operation, the fuel cell battery was kept at 100% relative humidity. 14. The system according to item 13, characterized in that the means of water supply include a pump and a control unit. 15. The system according to 14, characterized in that the control unit is equipped with a voltage sensor for measuring voltage on the fuel cell or battery of fuel cells. 16. The system of clause 15, wherein the control unit is a means for determining the maximum voltage of the fuel cell depending on the flow rate of the liquid phase of water for each of the many operating values of the currents of a standard fuel cell or battery of fuel cells. 17. The system according to item 13, characterized in that it contains a current sensor for measuring the electric current passing through the fuel cell or the battery of fuel cells, and means for regulating the water supply in such a way as to maintain the flow rate, providing the value of the water coefficient WF> 1 , 0 for all current values of the fuel cell or fuel cell battery in the region of their normal operation modes. 18. The system according to 17, characterized in that it includes means made with the possibility of regulating the supply of water with a flow rate that provides a water coefficient equal to at least 1.5. 19. The system according to p. 18, characterized in that it includes means made with the possibility of regulating the supply of water with a flow rate that provides a water coefficient of less than 40. 20. The system according to claim 19, characterized in that it includes means configured to control the water supply at a flow rate that provides a water coefficient of at least 3. 21. The system according to claim 20, characterized in that it includes means configured to control the water supply with a flow rate that provides a water coefficient in the range from 3 to 6. 22. The system according to any one of paragraphs.13-21, characterized in that it is additionally equipped with means for temporarily supplying to the flow grooves for the fluid, made in the cathode, such an amount of the liquid phase of the water so that the relative humidity is maintained at less than 100%, in the case when the temperature at the exit from the cathode is lower than a predetermined threshold value corresponding to an insufficiently optimal operating temperature.

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